2018 Fiji earthquakes

Last updated
2018 Fiji earthquakes
Fiji location map.svg
Bullseye1.png
Oceania laea relief location map.jpg
Bullseye1.png
UTC  time2018-08-19 00:19:40
 2018-09-06 15:49:18
ISC  event 616641704
  612848327
USGS-ANSS ComCat
  ComCat
Local dateAugust 19, 2018
 September 7, 2018
Local time12:19:40
 03:49:18
Magnitude8.2 Mww
 7.9 Mww
Depth600 km (370 mi)
 670.8 km (416.8 mi)
Epicenter 18°28′26″S179°21′00″E / 18.474°S 179.350°E / -18.474; 179.350
Type Normal
Oblique-slip
Total damageNone
Max. intensity MMI V (Moderate)
Tsunami15 cm (0.49 ft) [1]
Aftershocks575 (As of November 16 2018) [2]
CasualtiesNone

The 2018 Fiji earthquakes occurred on August 19, at 00:19:40 UTC and on September 6 15:49 UTC. The epicenters were located close to the Fijian island Lakeba, and around 270 km from the small town of Levuka on Ovalau. The first earthquake registered a magnitude of Mww  8.2, and is the largest earthquake of 2018. It had a focal depth of 600 km, making it the second largest earthquake ever recorded at a depth greater than 300 km; a tie with the 1994 Bolivia earthquake, and behind the 2013 Okhotsk Sea earthquake. The initial earthquake was caused by a normal fault below the South Pacific Ocean. [3] A Mww  7.9 event struck the islands again on September 6 at a depth of 670 km; this earthquake was a mainshock of its own. Both earthquakes may be considered a doublet event. [4]

Contents

Tectonic evolution

Initially, the Pacific Plate and the Indo-Australian Plate subducted, resulting in the heavier Pacific Plate to move beneath the Indo-Australian Plate. The subduction of the two plates resulted in the formation of a volcanic island arc called the Vityaz Arc. Twelve million years later, a similar event occurred. The Pacific plate converged towards the Indo-Australian plate at a north westward motion. Similarly, another volcanic island arc was formed near Fiji. The north westward motion continued to occur creating lots of stress on the plate boundary. Consequently, the Vityaz Arc was broken and the Fiji fracture zone was created. Recently, the movement of the plates created a subduction zone on the New Hebrides Trench. However, the Indo-Australian plate was pulled below the Pacific plate. The motion of these plates created a new volcanic island arc called the New Hebrides Arc. Eventually, the New Hebrides Arc and the Fiji islands started to diverge, which ultimately created the North Fiji Basin. [5]

Background

A notable earthquake in Fiji's history was one that occurred off the coast of Suva in 1953, as well as the 1979 Taveuni earthquake. The Suva earthquake of 1953 measured Ms  6.8, and was located off the southeastern coast of Viti Levu. The earthquake collapsed a coral reef platform and caused a tsunami. The earthquake, combined with the tsunami, took the lives of eight people and severely damaged a lot of architecture. The latter earthquake occurred in 1979 measuring Ms  6.9. While this event did not claim any lives, it caused major damage to buildings and triggered a major landslide on the island of Qamea. [6]

Earthquakes

Deep earthquakes are commonly defined as events occurring at a depth of 300 km or greater. These earthquakes occur within subducting slabs that are descending into the mantle. As these plates bend or flex, faults break out to accommodate the deformation and along with it, occasionally producing earthquakes. [7] Normally, deep earthquakes such as this one will not have too many aftershocks, however there are cases in which a deep earthquake produces much more than it should as if it were a shallow earthquake like Tonga in 1994. [8]

August 19

A cross-section diagram showing the Pacific slab under the Fijian Islands and the epicenters for both earthquakes. "Beach balls" are focal mechanism solutions marking the hypocenter locations of recorded earthquakes. Fiji 2018 doublet earthquakes diagram.png
A cross-section diagram showing the Pacific slab under the Fijian Islands and the epicenters for both earthquakes. "Beach balls" are focal mechanism solutions marking the hypocenter locations of recorded earthquakes.

Initially reported as an 8.0 earthquake, it was later revised by the United States Geological Survey to an 8.2. [9] Due to it being a deep-focus event, no damage was reported but it was widely felt. The undersea quake was too deep to trigger a large tsunami according to the US Pacific Tsunami Warning Center. [10] Small tsunami waves up to 15 cm (0.49 ft) high were spotted along the coast, [1] although it was too deep to generate more than a negligible tsunami. [11] [12] More than 250 aftershocks were recorded 34 days after the mainshock. The focal mechanism solution suggest the shock had a complex rupture process, and fast rupture velocity of 4.1 km/s. The rupture was observed along multiple faults in a mainly north-northeast-striking fault for a length of 102 to 152 km. [13] [14]

September 6

Eighteen days after the 8.2 event, another earthquake struck closer to the island of Viti Levu. The Mww 7.9 earthquake was a downgrade from an initial magnitude of 8.1. [15] [16] The earthquake had a complex combination of strike-slip and dip-slip during rupture within the slab. It was an unusual event as this portion of the downgoing slab is rather aseismic; not capable of producing earthquakes. The depth of this event was slightly deeper than the first quake, and the rupture velocity was much slower, at 2.5 km/s. [13] Coulomb stress transfer from the 8.2 quake may have triggered the 7.9 earthquake. However, stress from the first quake itself was not sufficient to generate the latter event. The Mww  7.9 event may have been dynamically triggered by the Mww  8.2 quake but the 18-day interval period was longer than usual as triggered quakes usually nucleate within a few hours to days. [13]

See also

Related Research Articles

<span class="mw-page-title-main">Cascadia subduction zone</span> Convergent plate boundary that stretches from northern Vancouver Island to Northern California

The Cascadia subduction zone is a 960 km (600 mi) fault at a convergent plate boundary, about 110–160 km (70–100 mi) off the Pacific coast, that stretches from northern Vancouver Island in Canada to Northern California in the United States. It is capable of producing 9.0+ magnitude earthquakes and tsunamis that could reach 30 m (98 ft). The Oregon Department of Emergency Management estimates shaking would last 5–7 minutes along the coast, with strength and intensity decreasing further from the epicenter. It is a very long, sloping subduction zone where the Explorer, Juan de Fuca, and Gorda plates move to the east and slide below the much larger mostly continental North American Plate. The zone varies in width and lies offshore beginning near Cape Mendocino, Northern California, passing through Oregon and Washington, and terminating at about Vancouver Island in British Columbia.

<span class="mw-page-title-main">Kamchatka earthquakes</span> Earthquakes in the Kamchatka Peninsula, far eastern Russia

Many major earthquakes have occurred in the region of the Kamchatka Peninsula in far eastern Russia. Events in 1737, 1923 and 1952, were megathrust earthquakes and caused tsunamis. There are many more earthquakes and tsunamis originating from the region.

The Sunda Trench, earlier known as and sometimes still indicated as the Java Trench, is an oceanic trench located in the Indian Ocean near Sumatra, formed where the Australian-Capricorn plates subduct under a part of the Eurasian Plate. It is 3,200 kilometres (2,000 mi) long with a maximum depth of 7,290 metres. Its maximum depth is the deepest point in the Indian Ocean. The trench stretches from the Lesser Sunda Islands past Java, around the southern coast of Sumatra to the Andaman Islands, and forms the boundary between the Indo-Australian Plate and Eurasian Plate. The trench is considered to be part of the alpida Belt as well as one of oceanic trenches around the northern edges of the Australian Plate.

<span class="mw-page-title-main">Aleutian Trench</span> An oceanic trench along the southern coastline of Alaska and the Aleutian islands

The Aleutian Trench is an oceanic trench along a convergent plate boundary which runs along the southern coastline of Alaska and the Aleutian islands. The trench extends for 3,400 kilometres (2,100 mi) from a triple junction in the west with the Ulakhan Fault and the northern end of the Kuril–Kamchatka Trench, to a junction with the northern end of the Queen Charlotte Fault system in the east. It is classified as a "marginal trench" in the east as it runs along the margin of the continent. The subduction along the trench gives rise to the Aleutian Arc, a volcanic island arc, where it runs through the open sea west of the Alaska Peninsula. As a convergent plate boundary, the trench forms part of the boundary between two tectonic plates. Here, the Pacific Plate is being subducted under the North American Plate at a dip angle of nearly 45°. The rate of closure is 7.5 centimetres (3 in) per year.

The 1953 Suva earthquake occurred on 14 September at 00:26 UTC near Suva, Fiji, just off the southeast shore of Viti Levu. This earthquake had an estimated magnitude of Ms 6.8 and Mw 6.4. The earthquake triggered a coral reef platform collapse and a submarine landslide that caused a tsunami. Eight people were reported killed; a wharf, bridges, and buildings were severely damaged in Suva.

The 2012 Indian Ocean earthquakes were magnitude 8.6 and 8.2 Mw  undersea earthquakes that struck near the Indonesian province of Aceh on 11 April at 15:38 local time. Initially, authorities feared that the initial earthquake would cause a tsunami and warnings were issued across the Indian Ocean; however, these warnings were subsequently cancelled. These were unusually strong intraplate earthquakes and the largest strike-slip earthquake ever recorded.

<span class="mw-page-title-main">2013 Solomon Islands earthquake</span> Megathrust earthquake and tsunami in Solomon Islands

The 2013 Solomon Islands earthquake struck Temotu Province within Solomon Islands on 6 February with a moment magnitude of 8.0 and a maximum Mercalli intensity of VIII (Severe). The epicentre was close to the Santa Cruz Islands within Temotu Province at the boundaries of the Indo-Australian and Pacific tectonic plates, causing local evacuations, a tsunami of 11 m (36 ft) and killing at least ten people.

The 2014 Iquique earthquake struck off the coast of Chile on 1 April, with a moment magnitude of 8.2, at 20:46 local time. The epicenter of the earthquake was approximately 95 kilometres (59 mi) northwest of Iquique. The mainshock was preceded by a number of moderate to large shocks and was followed by a large number of moderate to very large aftershocks, including a M7.7 event on 3 April. The megathrust earthquake triggered a tsunami of up to 2.11 metres (6.9 ft) that hit Iquique at 21:05 local time. Similar-sized tsunamis were also reported to have hit the coasts of Pisagua and Arica.

<span class="mw-page-title-main">Hikurangi Margin</span> Subduction zone off the east coast of New Zealands North Island

The Hikurangi Margin is New Zealand's largest subduction zone and fault.

The 1956 Amorgos earthquake occurred at 03:11 UTC on July 9. It had a magnitude of 7.7 on the moment magnitude scale and a maximum perceived intensity of IX on the Mercalli intensity scale. The epicentre was to the south of the island of Amorgos, the easternmost island of the Cyclades in the Aegean Sea. There was significant damage on Amorgos and the neighbouring island of Santorini. It was the largest earthquake in Greece in the 20th century. It was followed 13 minutes later by a magnitude 7.2 earthquake near Santorini. It triggered a major tsunami with a maximum run-up of 30 m. The combined effects of the earthquake shaking and the tsunami caused the deaths of 53 people with a further 100 injured.

<span class="mw-page-title-main">2016 Solomon Islands earthquakes</span> Seismic events

On 9 December 2016 at 4:38 a.m. local time, the Solomon Islands region was rocked by an Mww 7.8 earthquake, centred 30 km off San Cristobal Island, about 61 km southwest of Kirakira, the capital of Makira-Ulawa Province. Initially registering magnitude 8.0, later downgraded to 7.8, the temblor prompted tsunami warnings that kept countries surrounding the Coral, Tasman and Solomon Sea on high alert, but was later cancelled. A large aftershock of magnitude 6.9 occurred shortly afterwards. This earthquake was largely felt, waking many residents who later ran to high ground for fears of a potential tsunami. The earthquake killed a child and affected some 34,000 people in Makira, South Malaita and Guadalcanal Island where many had lost their homes or had no access to basic needs. Earthquakes are common in this region, with little or no fatalities. This earthquake is tied with three other magnitude 7.8 earthquakes for the second largest earthquake of 2016. On 17 December, Solomon Islands would be rattled again by a 7.9 magnitude earthquake, this time 54 km east of Taron, Papua New Guinea.

On July 17 2017, an earthquake struck near the Komandorski Islands, east of the Kamchatka Peninsula in the Bering Sea at. Although there were no casualties from this earthquake, it was notable for a rare characteristic known as supershear, and is one of the few times a large supershear earthquake has been observed. It was preceded by a few foreshocks months earlier, and aftershocks that continued for nearly six months.

<span class="mw-page-title-main">1993 Kushiro earthquake</span> Earthquake in Japan

The 1993 Kushiro–Oki earthquake was one of two large earthquake to strike the Japanese island of Hōkkaido within the same year. The earthquake with a magnitude of 7.6 Mw or 7.8 MJMA struck at 11:06 UTC or 08:06 pm JST on January 15 near the town of Ashoro. Shaking reached a maximum intensity of IX (Violent) on the Mercalli intensity scale, causing considerable damage, and was felt throughout the island, into northern Honshu, Sakhalin, and the Kuril Islands. As a result of the tremors, two people were killed and more than 600 were wounded.

The Nemuro-Oki earthquake in scientific literature, occurred on June 17 at 12:55 local time. It struck with an epicenter just off the Nemuro Peninsula in northern Hokkaidō, Japan. It measured 7.8–7.9 on the moment magnitude scale (Mw ), 8.1 on the tsunami magnitude scale (Mt ) and 7.4 on the Japan Meteorological Agency magnitude scale (MJMA ).

<span class="mw-page-title-main">2021 Chignik earthquake</span> 7th largest earthquake in the US

An earthquake occurred off the coast of the Alaska Peninsula on July 28, 2021, at 10:15 p.m. local time. The large megathrust earthquake had a moment magnitude of 8.2 according to the United States Geological Survey (USGS). A tsunami warning was issued by the National Oceanic and Atmospheric Administration (NOAA) but later cancelled. The mainshock was followed by a number of aftershocks, including three that were of magnitude 5.9, 6.1 and 6.9 respectively.

The 2021 Loyalty Islands earthquake was a 7.7 magnitude earthquake that struck offshore between Vanuatu and New Caledonia on February 11, 2021 at 00:19 local time. It is the 4th largest earthquake of 2021.

The 2021 South Sandwich Islands earthquakes were a pair of powerful earthquakes, followed by many strong aftershocks which struck along the South Sandwich Trench in August 2021. The quakes measured 7.5 and 8.1 on the moment magnitude scale, according to the United States Geological Survey. The mainshock is tied with another event in 1929 as the largest earthquake ever recorded in the South Atlantic region, and is tied with the 2021 Kermadec Islands earthquake as the second largest earthquake of 2021.

<span class="mw-page-title-main">2021 Flores earthquake</span> Earthquake in Indonesia

An earthquake occurred 112 km, offshore, north of Maumere in the Flores Sea on 14 December. The quake had a moment magnitude of 7.3 according to the United States Geological Survey (USGS). One person was killed and 173 others suffered injuries.

The 1843 Nias earthquake off the northern coast of Sumatra, Indonesia caused severe damage when it triggered a tsunami along the coastline. The earthquake with a moment magnitude (Mw ) of 7.8 lasted nine minutes, collapsing many homes in Sumatra and Nias. It was assigned a maximum modified Mercalli intensity of XI (Extreme).

References

  1. 1 2 "M 8.2 in Fiji on 19 Aug 2018 00:19 UTC". Global Disaster Alert and Coordination System .
  2. ↑ "USGS Earthquake Catalog". United States Geological Survey.
  3. ↑ "M 8.2 - 267 km E of Levuka, Fiji". earthquake.usgs.gov. Archived from the original on 2019-01-10. Retrieved 2021-10-13.
  4. ↑ Zhe Jia, Zhichao Shen, Zhongwen Zhan, Chenyu Li, Zhigang Peng, Michael Gurnis (2020). "The 2018 Fiji Mw 8.2 and 7.9 deep earthquakes: one doublet in two slabs". Earth and Planetary Science Letters. 531: 115997. Bibcode:2020E&PSL.53115997J. doi: 10.1016/j.epsl.2019.115997 .{{cite journal}}: CS1 maint: multiple names: authors list (link)
  5. ↑ "Plate Tectonic History of Fiji" (PDF). Mineral Resources Department. May 2015. Archived (PDF) from the original on 2018-08-27.
  6. ↑ Paterson, A. W.; Williams, R. L. (1980-06-30). "The Taveuni earthquake Fiji on 17 November 1979". Bulletin of the New Zealand Society for Earthquake Engineering. 13 (2): 194–201. doi: 10.5459/bnzsee.13.2.194-201 . ISSN   2324-1543.
  7. ↑ Houston, Heidi (December 2015). "Deep Earthquakes". Treatise on Geophysics: 329–354. doi:10.1016/B978-0-444-53802-4.00079-8. ISBN   9780444538031.
  8. ↑ Houston, H. (2015), "Deep Earthquakes", Treatise on Geophysics, Elsevier, pp. 329–354, doi:10.1016/b978-0-444-53802-4.00079-8, ISBN   978-0-444-53803-1 , retrieved 2021-10-13
  9. ↑ "Magnitude 8.2 quake strikes in the Pacific, no damage reported on Fiji". CNBC. 19 August 2018. Retrieved 4 December 2020.
  10. ↑ "Powerful magnitude 8.2 earthquake strikes in the Pacific near Tonga and Fiji". Stuff. August 20, 2018. Archived from the original on 2018-10-04.
  11. ↑ AP (19 August 2018). "8.2 earthquake strikes off the coast of Fiji, small tsunami waves observed". CBS. Retrieved 4 December 2020.
  12. ↑ "Earthquake of magnitude 8.2 strikes near Fiji, Tonga". Sydney Morning Herald. 19 August 2018. Retrieved 4 December 2020.
  13. 1 2 3 Wenyuan, Fan; Songqiao, Shawn Wei; Dongdong, Tian; McGuire, Jeffrey (February 2019). "Complex and Diverse Rupture Processes of the 2018 Mw8.2 and Mw 7.9 Tonga-Fiji Deep Earthquakes". Geophysical Research Letters.
  14. ↑ "Magnitude 8.2 quake strikes in the Pacific, no damage reported on Fiji". Reuters. August 18, 2018. Archived from the original on 2018-08-19. Retrieved December 1, 2021.
  15. ↑ "Deep magnitude 7.8 quake hits offshore from Suva, Fiji: USGS". The Straits Times. 7 September 2018. Retrieved 4 December 2020.
  16. ↑ NBC Staff (6 September 2020). "7.8M Earthquake Recorded Near Fiji". NCB San Diego. Retrieved 4 December 2020.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.